This invention relates to primary electrochemical cells. More particularly, it is concerned with primary electrochemical cells having an oxidizable active anode material, a cathode current collector, and an electrolytic solution comprising a reducible liquid cathode material and an electrolyte solute dissolved therein.
A particularly effective class of primary electrochemical cells which employs soluble or liquid cathode materials, as opposed to the more conventional solid cathode cells, has undergone rapid development in recent years. In these cells, the active cathode material is usually a fluid solvent for an electrolyte solute which provides conductivity. The active anode of these cells is usually lithium or other highly electropositive metal. During discharge, the solvent is electrochemically reduced on a cathode current collector to yield ions, e.g. halogen ions, which react with metallic ions from the anode to form soluble metal salts, e.g. metal halides. The cathode current collector does not take part in the reaction itself, but simply provides a support on which the reaction can occur, supplying electrons given up during the oxidation of the anode material.
A wide variety of materials have been employed to make up the cathode current collector or to provide a catalytically active surface thereof. For example, various cathode current collectors are described in U.S. Pat. Nos. 3,926,669 and 4,012,564 to Auborn. An improved cathode current collector and methods of making it are described in U.S. patent application Ser. No. 971,571 filed Dec. 20, 1978, by Keith A. Klinedinst and Francis G. Murphy now U.S. Pat. No. 4,219,443 issued Aug. 26, 1980 and assigned to the assignee of the present application. This application describes a cathode current collector having a surface layer of a finely divided catalyst for reducing the liquid cathode consisting of gold, platinum, or carbon black. Cathode current collectors employing a surface layer of platinum black to provide a catalytic surface have been found to provide very high discharge rates and current densities. However, electrochemical cells employing cathode current collectors with catalytic surface layers of platinum black are very expensive because of the cost of platinum and, therefore, uneconomical for many applications.